Flexxaire Manufacturing Inc. of Edmonton, Canada, manufactures a hydraulically controlled fan, and a pneumatically controlled fan. The pneumatic fan uses a single acting spring return piston, and the hydraulic fan uses a double acting piston. The current control systems for both fans have either two or three positions: full pitch and full reverse pitch, or full pitch, neutral and full reverse. A method of giving better control (partial pitch) is required. Both fans have similar difficulties, the force to pitch relationship has poor repeatability, high hysterisis, and is dependant on many variable factors (rpm, static pressure, blade length, and counterweight size). Both applications are cost sensitive.